Summary of work: GADD153 is a highly conserved mammalian gene whose expression is increased in response to a variety of stresses including growth arrest and DNA damage. It is a non-DNA binding member of the CCAAT/enhancer-binding protein (C/EBP) family of transcriptional activators, and has been proposed to serve as a negative regulator of other C/EBPs, by virtue of its ability to heterodimerize with them and inhibit their binding to DNA. Members of the C/EBP family are thought to play important roles in adipocyte differentiation and liver specific gene expression. Studies in our laboratory suggest that C/EBPs are also likely to serve a more ubiquitous role in regulating gene expression during stress. Studies in this project have focused on the regulation of GADD153 gene expression and the function of the GADD153 protein during the cellular response to diverse stresses. Efforts over the past year have concentrated on the role of a putative C/EBP binding site in the GADD153 promoter in regulating GADD153 transcription following arsenite treatment. In previous studies we had shown that C/EBP[unreadable] can transactivate the GADD153 promoter through binding to this site. Using electrophoretic gel mobility assays, immunoprecipitation reactions, Western analysis and functional assays utilizing transient transfection with CAT reporter systems, we have provided evidence that a number of other stress-responsive transcription factors also interact at this site to modulate GADD153 transcription. These include CREB2, ATF3 and JunD. Our findings indicate that CREB2 is a strong transactivator of GADD153 while ATF3 homodimers and ATF3-JunD heterodimers act as a transcriptional repressor of GADD153 expression. These data highlight the complexity of GADD153 regulation during the stress response and provide insight into the mechanisms that control the convergence of multiple transcription factor complexes at a single DNA-binding element.